JPH11334230A - Thermal transfer sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a thermal transfer sheet on which fog is not generated even on a high energy printing section and giving a highly sensitive transfer image. SOLUTION: A thermal transfer sheet is provided with a photothermal conversion layer containing a photothermal conversion substance and polyimide resin and an image forming layer, which contains 30-70 wt.% pigment and 30-70 wt.% non-crystalline organic polymer having its softening point in the range of 40-150 deg.C, in the thickness of 0.2-1.5 μm, formed successively on a substrate. In this case, the photothermal conversion substance contains an indolenine compound represented by a general formula. In the formula, Z represents an atomic group forming benzene rings and the like, R<1> and R<2> represents respectively and independently alkyl, alkenyl or aryl, and at least one group of them may form a ring in combination with L. L represents a trivalent connection group, and X<1> represents anion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer sheet used in an image forming method for forming a high-resolution image using a laser beam. In particular, the present invention relates to a color proof (DDCP: direct digital
Color proof) or a thermal transfer sheet that can be used in an image forming method useful for producing a mask image.

[0002]

2. Description of the Related Art In the field of graphic arts, a printing plate is printed using a set of color separation films prepared from a color original by using a lithographic film. In order to check for errors in the color separation process and the necessity of color correction beforehand, a color proof is produced from the color separation film. A color proof is desired to have high resolution which enables high reproducibility of a halftone image and high performance such as high process stability. In addition, in order to obtain a color proof similar to an actual printed matter, as a material used for a color proof, a material used for an actual printed matter, for example, a printing paper as a base material and a pigment as a coloring material are used. Is preferred. Also,
As a method for producing a color proof, there is a high demand for a dry method using no developer.

As a dry-type color proofing method, a recording system for directly producing a color proof from a digital signal has been developed with the recent spread of an electronic system in a pre-printing process (prepress field). In such an electronic system, it is necessary to produce a color proof having a particularly high image quality, and it is generally necessary to reproduce a halftone image of 150 lines / inch or more. In order to record a high-quality proof from a digital signal, it is necessary to use a laser beam which can be modulated by the digital signal and can narrow down the recording light as a recording head. For this reason, it is necessary to develop a recording material that exhibits high recording sensitivity to laser light and high resolution that enables high-definition halftone dots to be reproduced.

As a recording material used in a transfer image forming method using a laser beam, a photothermal conversion layer that absorbs a laser beam and generates heat, a wax and a binder in which a pigment is thermally fusible, and the like are provided on a support. (See Japanese Patent Laid-Open No. 5-58)
No. 045). In the image forming method using these recording materials, the heat generated in the laser light irradiation area of the light-to-heat conversion layer melts the image forming layer corresponding to the area, and is transferred onto the image receiving sheet stacked on the transfer sheet. Then, a transfer image is formed on the image receiving sheet.

Japanese Patent Application Laid-Open No. 6-219052 discloses that a light-to-heat conversion layer containing a light-to-heat conversion substance, a very thin (0.03-0.3 μm) heat-peeling layer, and a coloring material are provided on a support. An image forming layer including the image forming layer is provided in this order, the bonding force between the image forming layer and the light-to-heat conversion layer that are bonded by the interposition of the thermal peeling layer, using a thermal transfer sheet that is reduced by irradiation with laser light, An image forming method for forming a high-definition image on an image receiving sheet laminated on the thermal transfer sheet is described. This image forming method utilizes so-called "ablation". Specifically, the thermal peeling layer is partially decomposed and vaporized in a region irradiated with laser light, so that the image forming layer and the photothermal This utilizes the phenomenon that the bonding strength between the conversion layer and the image forming layer is weakened and the image forming layer in that region is transferred to the image receiving sheet laminated thereon.

In these image forming methods, printing paper having an image receiving layer (adhesive layer) attached thereto can be used as an image receiving sheet material, and multicolor images can be easily formed by transferring images of different colors onto the image receiving sheet one after another. In particular, the image forming method using ablation has an advantage that a high-definition image can be easily obtained, and has a color proof (DDCP: direct digital color proof) or a high color proof. It is useful for producing a fine mask image.

[0007] Since each layer of the thermal transfer sheet used in these image forming methods is formed by using a multi-layer coating method, it is desired that film formation of each layer be easy. The binder for the light-to-heat conversion layer, which is composed of a light-to-heat conversion material (a dye capable of absorbing laser light) and a binder, requires that the light-to-heat conversion material be easily dispersed and that it has excellent heat resistance. Is done. Conventionally, as a binder for the light-to-heat conversion layer, for example, as described in JP-A-5-58045 and JP-A-6-219052, homopolymers or copolymers of acrylic monomers such as acrylic acid are used. Coalesce, cellulosic polymer such as cellulose acetate, polystyrene, vinyl chloride / vinyl acetate copolymer, vinyl polymer such as polyvinyl butyral, polyvinyl alcohol, condensation polymer such as polyester and polyamide, butadiene / styrene copolymer Rubber thermoplastic polymers, polyurethanes, epoxy resins, urea / melamine resins and the like are mentioned. Of these, polymers such as polyvinyl alcohol, polyvinyl butyral, and polyester are usually preferably used.

However, according to the study of the present inventors,
A light-to-heat conversion layer using a water-soluble polymer such as polyvinyl alcohol generally has poor moisture resistance, and when stored under high temperature and high humidity for a long time, agglomeration of dyes may occur. Further, in the photothermal conversion layer using a polyvinyl butyral, a polyester resin, or the like, in which the above-described phenomenon is relatively unlikely to occur,
The heat-sensitive release layer coating solution applied to the surface of the light-to-heat conversion layer, or the light-to-heat conversion layer is immersed in the solvent contained in the image-forming layer coating solution, and the light-to-heat conversion material contained in the light-to-heat conversion layer migrates to these layers. As a result, the performance of the light-to-heat conversion layer (for example,
(Sensitivity) and fog sometimes occurred.
In addition, these polymers do not have sufficient heat resistance, and therefore are liable to undergo thermal decomposition and thermal fusion during laser recording, whereby part of the light-to-heat conversion layer is transferred together with the image forming layer, and a good image cannot be obtained. In some cases, the transcription operation was inhibited. Therefore, in order to prevent these adverse effects, it is conceivable to use a heat-resistant polymer such as a polyimide resin, but when using a conventionally known photothermal conversion substance and a photothermal conversion layer containing these polymers, Although an antifogging effect is observed, further improvement has been desired.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermal transfer sheet which is free of fog even in a high energy printing portion and gives a transfer image with high sensitivity.

[0010]

Means for Solving the Problems The present inventor has conducted research on a light-to-heat conversion material suitable for a light-to-heat conversion layer. According to this, the light-to-heat conversion layer in which a polyimide resin and a light-to-heat conversion material having a high light-to-heat conversion ability are combined does not cause performance deterioration or fog of the light-to-heat conversion layer due to migration of the light-to-heat conversion material as described above, and It has been found that a transfer image with high sensitivity can be formed.

That is, the present invention provides: <1> a photothermal conversion layer containing a photothermal conversion substance and a polyimide resin on a support, an amorphous organic polymer having a pigment and a softening point in a temperature range of 40 to 150 ° C. 30 polymers each
In a thermal transfer sheet provided with an image forming layer having a thickness of 0.2 to 1.5 microns in this order, the photothermal conversion substance is an indolenine-based compound represented by the following general formula (I). A thermal transfer sheet characterized by being a compound.

[0012]

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[0013] (wherein, Z is represents an atomic group for forming a benzene ring, a naphthalene ring or heterocyclic aromatic ring, R ¹
And R ² each independently represent an alkyl group, an alkenyl group or an aryl group, and at least one of these groups may be connected to L to form a ring. L represents a trivalent linking group, and X ⁻ represents an anion. <2> L which is a trivalent linking group in the general formula (I) is
The thermal transfer sheet according to <1>, which is an indolenine compound represented by the following general formula (L-1) or (L-2).

[0014]

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(In the formula, Y represents a hydrogen atom or a monovalent group.) <3> The above <1> or <2> wherein a heat-sensitive release layer is provided between the photothermal conversion layer and the image forming layer. <2> The thermal transfer sheet described in (1).

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the materials constituting the thermal transfer sheet of the present invention will be described. The thermal transfer sheet of the present invention has a light-to-heat conversion layer and an image forming layer on a support, and further has other layers such as a heat-sensitive release layer, if necessary. [Support] The material of the support of the thermal transfer sheet is not particularly limited, and various support materials can be used according to the purpose. Preferred examples of the support material include synthetic resin materials such as polyethylene terephthalate, polyethylene-2,6-naphthalate, polycarbonate, polyethylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, and styrene-acrylonitrile copolymer. . Among them, biaxially stretched polyethylene terephthalate is preferable in consideration of mechanical strength and dimensional stability against heat. When the thermal transfer sheet of the present invention is used for producing a color proof using laser recording, the support of the thermal transfer sheet is preferably formed of a transparent synthetic resin material that transmits laser light.

The support of the thermal transfer sheet may be subjected to a surface activation treatment and / or the provision of one or more undercoat layers in order to improve the adhesion to the light-to-heat conversion layer provided thereon. Is preferred. Examples of the surface activation treatment include a glow discharge treatment and a corona discharge treatment. The material of the undercoat layer preferably has high adhesiveness to both surfaces of the support and the light-to-heat conversion layer, low thermal conductivity, and excellent heat resistance. Examples of such a material for the undercoat layer include styrene, styrene-butadiene copolymer, and gelatin.
The thickness of the entire undercoat layer is usually 0.01 to 2 μm. Further, on the surface of the thermal transfer sheet opposite to the side on which the light-to-heat conversion layer is provided, various functional layers such as an anti-reflection layer can be provided or surface treatment can be performed, if necessary.

[Light-to-heat conversion layer] The light-to-heat conversion layer contains a light-to-heat conversion material and a polyimide resin, and further contains other components as necessary. (Light-to-heat conversion material) The light-to-heat conversion material contained in the light-to-heat conversion layer will be described. The light-to-heat conversion substance used in the present invention is characterized by having a high light-to-heat conversion ability.
Such a light-to-heat conversion material is specifically represented by the following general formula
It is an indolenine compound represented by (I).

[0019]

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In the above formula, examples of the ring completed by Z include a benzene ring, a naphthalene ring, a pyridine ring, a quinoline ring, a pyrazine ring and a quinoxaline ring. Further, another substituent R ³ may be bonded on Z. Examples of such a substituent R ³ include an alkyl group, an aryl group, a heterocyclic residue, a halogen atom, an alkoxy group, an aryloxy group, an alkylthio group,
Arylthio group, alkylcarbonyl group, arylcarbonyl group, alkyloxycarbonyl group, aryloxycarbonyl group, alkylcarbonyloxy group, arylcarbonyloxy group, alkylamide group, arylamide group, alkylcarbamoyl group, arylcarbamoyl group, alkylamino group An arylamino group, a carboxylic acid group, an alkylsulfonyl group, an arylsulfonyl group, an alkylsulfonamide group, an arylsulfonamide group,
Examples include various substituents such as an alkylsulfamoyl group, an arylsulfamoyl group, a cyano group, and a nitro group. The number (p) of the substituents bonded on Z is usually preferably 0 or about 1 to 4. Note that p
Is 2 or more, a plurality of R ³ may be the same or different.

Among the substituents represented by R ³ , a halogen atom (for example, F, Cl, etc.), a cyano group, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms (for example,
A methoxy group, an ethoxy group, a dodecyloxy group, a methoxyethoxy group, etc., a substituted or unsubstituted phenoxy group having 6 to 20 carbon atoms (for example, phenoxy group, 3,5-
Dichlorophenoxy group, 2,4-di-t-pentylphenoxy group, etc.), substituted or unsubstituted carbon atoms having 1 to 2 carbon atoms.
0 alkyl group (for example, methyl group, ethyl group, isobutyl group, t-pentyl group, octadecyl group, cyclohexyl group, etc.), substituted or unsubstituted phenyl group having 6 to 20 carbon atoms (for example, phenyl group, 4 -Methylphenyl group, 4-trifluoromethylphenyl group, 3,5-dichlorophenyl group and the like).

R ¹ and R ² represent an alkyl group, alkenyl group or aryl group having 1 to 20 carbon atoms, which may be the same or different. R ¹ and R
² may each further have a substituent. Among the substituents in these groups, C. Hansch
Π which is a hydrophobicity parameter proposed by
Is preferably in the range of -1.0 to 15. The hydrophobic parameter π can be calculated according to the following literature. (1) Sheehansch, Journal of Medical
Chemistry (C. Hansch, J. Med. Chem.), Volume 16,
1207 (1973), (2) See Hansch (C.
Hansch), same magazine, vol. 20, p. 304 (1977) R
¹ and R ² are a substituted or unsubstituted phenyl group, a substituted or unsubstituted lower alkyl group having 1 to 8 carbon atoms,
Alternatively, a substituted or unsubstituted lower alkenyl group having 2 to 8 carbon atoms is preferable, and the hydrophobic parameter π of these substituents is preferably in the range of -1.0 to 15.

Examples of the substituent on R ¹ and R ² include a halogen atom (F, Cl, Br and I), a substituted or unsubstituted phenyl group (for example, phenyl, m-chlorophenyl and p-methylphenyl). Group), an alkylthio group (eg, a methylthio group and a butylthio group), a substituted or unsubstituted phenylthio group (eg, a phenylthio group, a p-chlorophenylthio group, an m-methylphenylthio group, and the like), and an alkoxy group (eg, Ethoxy group and butoxy group, etc.). R ¹ and R ² are particularly preferably an unsubstituted alkyl group having 2 to 8 carbon atoms or an unsubstituted alkenyl group having 2 to 8 carbon atoms.

L represents a trivalent linking group, and is formed by connecting a trivalent substituted or unsubstituted methine group or 3, 5, or 7 substituted or unsubstituted methine groups by a conjugated double bond. It is preferably a conjugated linking group,
Groups represented by the following (L-1) to (L-9) are preferred.

[0025]

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Y in the formulas (L-1) to (L-9) represents a hydrogen atom or a monovalent group. Examples of such a monovalent group include a lower alkyl group such as a methyl group, an aralkyl group such as a substituted or unsubstituted phenyl group and a benzyl group, a lower alkoxy group such as a methoxy group, a dimethylamino group, a diphenylamino group, a methyl group. Phenylamino group, morpholino group, disubstituted amino group such as imidazolidino group and ethoxycarbonylpiperazino group, alkylcarbonyloxy group such as acetoxy group, alkylthio group such as methylthio group,
Preference is given to cyano groups, nitro groups and halogen atoms such as F, Cl, Br and the like. Among the linking groups represented by L in the general formula (I), the groups represented by (L-1) and (L-2) are most preferred.

X in the general formula (I)^-Is the cation part
Provides the necessary number of negative charges to neutralize the charge
And represents a monovalent or divalent anion. X above^-
As Cl^-, Br^-, I^-Halogen ions such as
SO^2-, HSO^-, CH_ThreeOSO_Three ^-Such as alkyl sulfur
Acid ion, p-toluenesulfonic acid ion, naphthalene
-1,5-disulfonate ion, methanesulfonic acid ion
, Trifluoromethanesulfonic acid ion, octance
Sulfonate ion, p-chlorobenzoate ion, triflu
Oroacetate ion, oxalate ion, succinate ion, etc.
Carboxylate ion, PF₆ ^-, BF_Four ^-, ClO_Four ^-,
IO_Four ^-, Tungstate ion, tungstophosphate
Heteropolyacid ion such as on, H_TwoPO_Four ^-, N
O _Three ^-And phenolate ions such as picrate ion
preferable. Among these, Cl^-, Br^-, I^-Etc.
Rogen ion, CH_ThreeOSO_Three ^-, C_TwoH_FiveOS
O_Three ^-, Paratoluenesulfonic acid ion, trifluoro
Methanesulfonic acid ion, P-chlorobenzenesulfone
Acid ion, methanesulfonic acid ion, butanesulfonic acid
Ion, naphthalene-1,5-disulfonic acid ion,
Perfluoros such as trifluoromethanesulfonic acid ion
Sulfonate ion, PF^-, BF^-, ClO^-Etc. are better
Preferably, among these, trifluoromethanesulfonic acid
Ion, PF₆ ^-, ClO_Four ^-And the like are particularly preferred.

Specific examples of the indolenine compound represented by the general formula (I) include, but are not limited to, the following compounds.

[0029]

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[0030]

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[0031]

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The crosslinked indolenine compound represented by the general formula (I) can be easily synthesized usually in the same manner as when synthesizing a carbocyanine dye. That is, the heterocyclic enamine is converted to CH ₃ O—CH ＝ CH—CH
Acetals such as ＝ CH—CH (OCH ₃ ) ₂ or P
The compound can be easily synthesized by reacting with a compound represented by hN-CH- (CH-CH) -NHPh. Here, Ph represents a phenyl group. In addition, for the synthesis method of these compounds, see, for example, JP-A-5-11-11.
Reference can be made to the description of JP-A-6450.

In the present invention, the indolenine compound represented by the general formula (I) is contained as a main component of the photothermal conversion substance. A light-to-heat conversion material may be contained. Conventionally known photothermal conversion substances are generally dyes (eg, pigments) capable of absorbing laser light. Examples of such dyes (eg, pigments) include black pigments such as carbon black, Phthalocyanine, macrocyclic compound pigments having absorption in the visible to near infrared region, such as naphthalocyanine,
Organic dyes (cyanine dyes other than indolenine dyes according to the present invention, anthraquinone dyes, azulene dyes, phthalocyanine dyes) used as laser absorbing materials for high-density laser recording such as optical disks, and organic dyes such as dithiol nickel complexes Metal compound dyes are exemplified.

(Polyimide resin) The polyimide resin used in the photothermal conversion layer is preferably a polyimide resin soluble in a solvent, and examples thereof include the following.

[0035]

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In the formulas (II) and (III), Ar ¹ is represented by the formula (1)
Represents an aromatic group represented by (3), wherein n is 10 to 10
Indicates an integer of 0.

[0037]

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[0038]

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In the formulas (IV) and (V), Ar ² is represented by the formula (4)
Represents an aromatic group represented by (7), and n is 10 to 100
Indicates an integer.

[0040]

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In the present invention, as a guide for judging that the polyimide resin is soluble in a solvent, at 25 ° C., 100 parts by weight of N-methylpyrrolidone is added to the polyimide resin.
It is based on melting at least 10 parts by weight and is preferably used in the present invention. More preferably, 100 parts by weight or more of the polyimide resin is dissolved with respect to 100 parts by weight of N-methylpyrrolidone. In the present invention, a polyimide resin soluble in the above-mentioned solvent is preferably used, but other conventionally known polyimide resins can also be used. The glass transition temperature of the polyimide resin is 200 ° C. or higher and 4
The temperature is preferably not higher than 00 ° C. Further, the 5% weight loss temperature of the polyimide resin measured by the TDA method is 450 ° C.
It is preferable that it is above.

(Formation of Light-to-Heat Conversion Layer) The light-to-heat conversion layer can be provided by preparing a coating solution in which a light-to-heat conversion material and a polyimide resin are dissolved, coating the solution on the support, and drying. As an organic solvent for dissolving the polyimide resin, for example, 1,4-dioxane, 1,
3-dioxolan, dimethyl acetate, N-methyl-
2-pyrrolidone, dimethylsulfoxide, dimethylformamide, dimethylacetamide, γ-butyrolactone, and the like. Coating and drying can be performed by using ordinary coating and drying methods.

In the light-to-heat conversion layer formed as described above, the solid content weight ratio of the light-to-heat conversion substance (dye) to the polyimide resin is in the range of 1:20 to 2: 1 (light-to-heat conversion substance: polyimide resin). It is particularly preferable that the ratio be in the range of 1:10 to 2: 1. If the amount of the polyimide resin is too small, the cohesive force of the light-to-heat conversion layer is reduced, and when the formed image is transferred to the image receiving sheet, the light-to-heat conversion layer is easily transferred together, causing color mixing of the image. On the other hand, if the amount of the polyimide resin is too large, the thickness of the light-to-heat conversion layer becomes large in order to achieve a constant light absorptivity, which tends to cause a decrease in sensitivity. The layer thickness of the light-to-heat conversion layer is preferably from 0.03 to 0.8 μm, more preferably from 0.05 to 0.3 μm. The light-to-heat conversion layer has a thickness of 700 to 2000 nm.
In the wavelength range of 0.1 to 1.3 (more preferably,
It preferably has a maximum absorbance (optical density) of 0.2 to 1.1).

Since the polyimide resin contained in the light-to-heat conversion layer is excellent in heat resistance (for example, heat deformation temperature and thermal decomposition temperature), the conditions required for the binder (for the layer provided on the light-to-heat conversion layer, Higher than the heat resistance of the material used). In the present invention,
Since a polyimide resin is used as the binder, there is also an advantage that the viscosity stability, long-term storage property, and moisture resistance of the coating solution due to the properties of the resin are improved.

[Thermal Release Layer] On the light-to-heat conversion layer of the thermal transfer sheet of the present invention, a gas is generated by the action of heat generated in the light-to-heat conversion layer, or adhered water or the like is released. A heat-sensitive release layer containing a heat-sensitive material that reduces the bonding strength between the heat-sensitive adhesive and the image forming layer. Examples of such a heat-sensitive material include a compound (polymer or low-molecular compound) that decomposes or deteriorates by heat to generate a gas, and a compound (polymer) that absorbs or adsorbs a considerable amount of easily vaporizable gas such as moisture. Or a low molecular compound). These may be used in combination.

Examples of the polymer which decomposes or degrades by heat to generate a gas include self-oxidizing polymers such as nitrocellulose, chlorinated polyolefin, chlorinated rubber, polyvinyl chloride, polyvinyl chloride, polyvinylidene chloride, and the like. Such a halogen-containing polymer, an acrylic polymer such as polyisobutyl methacrylate in which a volatile compound such as moisture is adsorbed, a cellulose ester such as ethyl cellulose in which a volatile compound such as water is adsorbed, and a volatile compound such as water. Examples thereof include natural polymer compounds such as adsorbed gelatin. Examples of the low molecular weight compound which decomposes or degrades by heat to generate a gas include a compound which generates a gas upon exothermic decomposition such as a diazo compound or azide. It is preferable that the heat-sensitive material is decomposed or deteriorated by heat at 280 ° C. or lower, particularly at 230 ° C. or lower.

When a low-molecular compound is used as the heat-sensitive material of the heat-sensitive release layer, it is desirable to combine it with a binder. As the binder, the above-mentioned polymer which itself decomposes or degrades by heat to generate a gas can be used, but an ordinary polymer binder having no such properties can also be used. When a heat-sensitive low-molecular compound and a binder are used in combination, the weight ratio of the former to the latter is preferably 0.02: 1 to 3: 1, more preferably 0.05: 1 to 2: 1. Is more preferred. The heat-sensitive peeling layer desirably covers the light-to-heat conversion layer over substantially the entire surface thereof, and generally has a thickness of 0.03 to 1 μm, preferably 0.05 to 0.5 μm.

On a support, a light-to-heat conversion layer, a heat-sensitive release layer,
In the case of a thermal transfer sheet having a configuration in which the image forming layers are laminated in this order, the heat-sensitive release layer decomposes and degrades by the heat transmitted from the light-to-heat conversion layer to generate gas. Then, due to the decomposition or generation of gas, the heat-sensitive peeling layer partially disappears, or cohesive failure occurs in the heat-sensitive peeling layer, and the bonding force between the light-heat conversion layer and the image forming layer decreases. For this reason, depending on the behavior of the heat-sensitive release layer, a part of the heat-sensitive release layer may adhere to the image forming layer and appear on the surface of a finally formed image, which may cause color mixing of the image. Therefore, even when such transfer of the heat-sensitive release layer occurs, the heat-sensitive release layer is hardly colored, that is, high in visible light, so that no visual color mixture appears in the formed image. It is desirable to show permeability. Specifically, the light absorption of the heat-sensitive peeling layer is 50% or less, preferably 1 to visible light.
0% or less. Note that, in the thermal transfer sheet of the present invention, instead of providing an independent heat-sensitive release layer, the above-mentioned heat-sensitive material is added to a light-heat conversion layer coating solution to form a light-heat conversion layer, and the light-heat conversion layer and the heat-sensitive release layer are formed. It is also possible to adopt a configuration that also serves as a combination.

[Image Forming Layer] In the thermal transfer sheet of the present invention, the image forming layer is provided on the light-to-heat conversion layer or, if desired, the heat-sensitive peeling layer provided thereon. The image forming layer contains a pigment and an amorphous organic high molecular polymer, and further contains other components as necessary.

(Pigments) Pigments are generally classified into organic pigments and inorganic pigments. The former is particularly excellent in the transparency of a coating film, and the latter is generally excellent in hiding. When the thermal transfer sheet of the present invention is used for printing color proofing, an organic pigment that matches or has a similar color tone to yellow, magenta, cyan, and black generally used for printing inks is preferably used.
In addition, a metal powder, a fluorescent pigment, or the like may be used. Examples of preferably used pigments include azo pigments,
Examples include phthalocyanine pigments, anthraquinone pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, and nitro pigments. The following is a description of representative pigments classified by hue.

1) Yellow pigments Hansa Yellow G, Hansa Yellow 5G, Hansa Yellow 10G, Hansa Yellow A, Pigment Yellow L,
Permanent Yellow NCG, Permanent Yellow F
GL, permanent yellow HR. 2) red pigment permanent red 4R, permanent red F2R,
Permanent Red FRL, Lake Red C, Lake Red D, Pigment Scarlet 3B, Bordeaux 5B,
Alizarin Lake, Rhodamine Lake B. 3) Blue pigments Phthalocyanine blue, Victoria blue lake, Fast sky blue. 4) Black pigment carbon black.

(Amorphous Organic High Polymer) The softening point of the thermal transfer sheet of the present invention is 40 ° C. to 1 which is contained in the image forming layer.
Examples of the amorphous organic high-molecular polymer at 50 ° C. include butyral resin, polyamide resin, polyethyleneimine resin, sulfonamide resin, polyester polyol resin, petroleum resin, styrene, vinyltoluene, α-methylstyrene, and 2-methylstyrene. Styrene and its derivatives, such as chlorostyrene, vinylbenzoic acid, sodium vinylbenzenesulfonate, and aminostyrene; substituted homopolymers and copolymers; methacrylic acid such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, and hydroxyethyl methacrylate Esters and acrylates such as methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate and α-ethylhexyl acrylate; and dienes such as acrylic acid, butadiene and isoprene; Use of vinyl monomers such as acrylonitrile, vinyl ethers, maleic acid and maleic acid esters, maleic anhydride, cinnamic acid, vinyl chloride, vinyl acetate, or copolymers with other monomers be able to. These resins can be used as a mixture of two or more kinds. In the invention, the image forming layer contains 3 pigments.
0 to 70% by weight, preferably 40 to 60% by weight, and 70 to 30% by weight, preferably 60 to 60% by weight of the amorphous organic high molecular polymer.
-40% by weight.

(Other Components) When a multicolor image is produced by repeatedly superimposing a number of image layers (image forming layers on which images are formed) on the same image receiving sheet using the thermal transfer sheet of the present invention. Preferably, the image forming layer contains a plasticizer in order to enhance the adhesion between images. Examples of such plasticizers include phthalates such as dibutyl phthalate, di-n-octyl phthalate, di (2-ethylhexyl phthalate, dinonyl phthalate, dilauryl phthalate, butyllauryl phthalate, butylbenzyl phthalate, etc. Acid esters,
Aliphatic dibasic acid esters such as di (2-ethylhexyl) adipate and di (2-ethylhexyl) sebacate;
Examples include phosphoric acid triesters such as tricresyl phosphate and tri (2-ethylhexyl) phosphate, polyol polyesters such as polyethylene glycol ester, and epoxy compounds such as epoxy fatty acid ester. Also,
In addition to the above general plasticizers, polyethylene glycol dimethacrylate, 1,2,4-butanetriol trimethacrylate, trimethylolethane triacrylate, pentaerythritol triacrylate, pentaerythrite tetraacrylate, dipentaerythrate Acrylic esters such as trit-polyacrylate are also suitably used depending on the type of binder used. Incidentally, two or more plasticizers may be used in combination.

In the image forming layer, the weight ratio of the total amount of the pigment and the amorphous organic polymer to the plasticizer is generally 100: 1 to 100: 3, preferably 10: 1.
It is used so as to be in the range of 0: 1.5 to 100: 2. The above-mentioned. . In addition to the amount, a surfactant, a thickener, and the like are further added as necessary. The layer thickness (dry layer thickness) of the image forming layer is 0.2 to 1.5 μm, preferably 0.3 to 1.0 μm.

[Image-Receiving Sheet] To prevent damage, an image-receiving sheet or a protective cover film (eg, polyethylene terephthalate sheet, polyethylene sheet, etc.) is usually laminated on the surface of the image forming layer. The image receiving sheet is usually
One or two or more image receiving layers are provided on a usual sheet-like base material such as a plastic sheet, a metal sheet, a glass sheet, and paper. Examples of the plastic sheet include a polyethylene terephthalate sheet, a polycarbonate sheet, a polyethylene sheet, a polyvinyl chloride sheet, a polyvinylidene chloride sheet, a polystyrene sheet, and a styrene-acrylonitrile sheet. As the paper, printing paper, coated paper, or the like can be used. The thickness of the base material of the image receiving sheet is usually 10
４００400 μm, preferably 25-200 μm. The surface of the substrate may be subjected to a surface treatment such as a corona discharge treatment or a glow discharge treatment in order to enhance the adhesion to the image receiving layer or the adhesion to the image forming layer of the thermal transfer sheet.

In order to assist in transferring and fixing the image forming layer on the surface of the image receiving sheet, it is preferable to provide one or two or more image receiving layers on the surface of the substrate as described above. The image receiving layer is a layer formed mainly of an organic polymer binder. The binder is preferably a thermoplastic resin, and examples thereof include acrylic acid, methacrylic acid, acrylic acid esters, homopolymers of acrylic monomers such as methacrylic acid esters and copolymers thereof, methylcellulose, ethylcellulose, and cellulose acetate. Cellulose polymers such as polystyrene, polyvinylpyrrolidone, polyvinyl butyral, homopolymers of vinyl monomers such as polyvinyl alcohol and copolymers thereof, polyesters, condensation polymers such as polyamides, butadiene-styrene copolymers And rubber-based polymers such as The binder of the image receiving layer is preferably a polymer having a glass transition temperature (Tg) lower than 90 ° C. in order to obtain a proper adhesive strength with the image forming layer. Further, it is preferable to add a plasticizer to the image receiving layer in order to adjust the glass transition temperature of the image receiving layer.

After the image is once formed on the image receiving sheet by transfer,
When this is transferred to separately prepared printing paper or the like, it is desirable that at least one of the image receiving layers, particularly the uppermost layer, is formed of a photocurable material. Examples of the composition of such a photocurable material include: a) a photopolymerizable monomer comprising at least one kind of a polyfunctional vinyl or vinylidene compound capable of forming a photopolymer by addition polymerization; b) an organic polymer binder; ) Combinations of photopolymerization initiators and, if necessary, additives such as thermal polymerization inhibitors. Examples of the above polyfunctional vinyl compound and vinylidene compound include unsaturated esters of polyols, especially esters of acrylic acid or methacrylic acid (for example, ethylene glycol diacrylate, glycerin triacrylate, ethylene glycol dimethacrylate, 1,3-propane). Diol dimethacrylate, polyethylene glycol dimethacrylate, 1,2,4-butanetriol trimethacrylate, trimethylolethane triacrylate, pentaerythritol dimethacrylate, pentaerythritol trimethacrylate, pentaerythrit tetramethacrylate, pentaerythritol diacrylate, Pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol-polyacrylate, , 3-propanediol-diacrylate, 1,5-pentanediol-dimethacrylate, bisacrylates and bismethacrylates of polyethylene glycol having a molecular weight of 200 to 400), unsaturated amides, especially whose alkylene chains are opened by carbon atoms. Unsaturated amides of acrylic acid and methacrylic acid having an α, ω-diamine which may be present, and ethylenebismethacrylamide. Further, a polyester acrylate obtained by condensing an ester of a polyhydric alcohol and a polyvalent organic acid with acrylic acid or methacrylic acid can also be used.

As the organic polymer binder, the above-mentioned thermoplastic resin binder for forming the image receiving layer is suitably used. The photopolymerizable monomer and the organic polymer binder generally have a weight ratio of 0.1: 1.0 to 2.0:
It is used in the range of 1.0. As the photopolymerization initiator, those having absorption in the near ultraviolet region and no absorption in the visible region (or low absorption in the visible region) are used. Examples of such photopolymerization initiators include benzophenone, Michler's ketone [4,4'-bis (dimethylamino) benzophenone], 4-methoxy-4'-dimethylaminobenzophenone, 2-ethylanthraquinone, and phenonetraquinone. Aromatic ketones, benzoin ethers such as benzoin, benzoin methyl ether, benzoin ethyl ether and benzoin phenethyl ether; benzoins such as methyl benzoin and ethyl benzoi; and 2- (ο-chlorophenyl) -4,5-diphenylimidazole Examples of the dimer include 2- (o-chlorophenyl) -4,5- (m-methoxyphenyl) imidazole dimer. The photopolymerization initiator is generally 0.1 to 100 parts by weight of the photopolymerizable monomer.
It is used in an amount in the range of 20 parts by weight.

The laminate of the thermal transfer sheet and the image receiving sheet of the present invention can be easily formed by superposing the image forming layer side of the thermal transfer sheet and the image receiving side (image receiving layer side) of the image receiving sheet and passing them through a pressure and heating roller. Can be obtained. The heating temperature in this case is preferably 130 ° C. or less, and 100 ° C.
It is more preferable to set the following.

[Image Forming Method] Next, an image forming method using the thermal transfer sheet of the present invention will be described. In the image forming method using the thermal transfer sheet of the present invention, an image forming laminate in which an image receiving sheet is laminated on the surface of the image forming layer of the thermal transfer sheet is prepared, and the surface of the laminate is irradiated with laser light in an image-wise manner. Then, the image receiving sheet and the thermal transfer sheet are separated from each other to obtain an image receiving sheet on which the laser light irradiated area of the image forming layer has been transferred. The joining of the thermal transfer sheet and the image receiving sheet may be performed immediately before the laser beam irradiation operation. In this laser beam irradiation operation, usually, the image receiving sheet side of the image forming laminate is placed on a recording drum (a rotary drum having a vacuum forming mechanism inside and a large number of minute openings on the surface).
The heat transfer sheet is irradiated with laser light from the outside, that is, from the side of the thermal transfer sheet in this state. The laser beam is scanned so as to reciprocate in the width direction of the drum, and the drum is rotated at a constant angular velocity during the irradiation operation.

The laser light may be a gas laser light such as an argon ion laser light, a helium neon laser light, a helium cadmium laser light, a solid laser light such as a YAG laser light, a semiconductor laser, a dye laser light, an excimer laser light or the like. Laser light is used. Alternatively, light or the like obtained by converting these laser lights to half the wavelength through a second harmonic element can be used. In the image forming method using the thermal transfer sheet of the present invention, it is preferable to use a semiconductor laser in consideration of output power, ease of modulation, and the like. Further, in the image forming method using the thermal transfer sheet of the present invention, it is preferable that the laser beam is irradiated under conditions such that the beam diameter on the light-to-heat conversion layer is in the range of 5 to 50 μm (particularly 6 to 30 μm), The scanning speed is 1m /
It is preferably at least 2 seconds (particularly at least 3 m / second).

The image forming method using the thermal transfer sheet of the present invention can be used for producing a black mask or for forming a monochromatic image, but can also be advantageously used for forming a multi-color image. In order to form a multi-color image by the image forming method using the thermal transfer sheet of the present invention, for example, three types (three colors) or three types (three colors) of image forming laminates having image forming layers containing colorants of different colors are independently provided. Four types (four colors)
Manufacture, laser light irradiation according to digital signal based on image by color separation filter, peeling operation of image recording transfer sheet and image receiving sheet for each, and color separation image of each color is formed on each image receiving sheet independently Then, a method of sequentially laminating the respective color-separated images on an actual support such as a separately prepared printing paper or a similar support may be used.

[0063]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. “Parts” are “parts by weight” unless otherwise noted in the text.
Means (Example 1) 1) Preparation of coating solution for photothermal conversion layer The following components were mixed while stirring with a stirrer to prepare a coating solution for the photothermal conversion layer. [Coating liquid composition] 10 parts of photothermal conversion substance (compound represented by the above general formula (I-3)) 200 parts of polyimide resin (Ricacoat SN-20, manufactured by Shin Nippon Rika Co., Ltd.) 200 parts N-methyl- 2-pyrrolidone 2,000 parts-Surfactant (MegaFac F-177, Dainippon Ink and Chemicals 1 part, Industrial Co., Ltd.)

2) Formation of a light-to-heat conversion layer on the surface of the support The above-mentioned coating solution was coated on one surface of a 100 μm-thick polyethylene terephthalate film using a rotary coating machine (wheeler), and then the coated material was coated. After drying in an oven at 100 ° C. for 2 minutes, a light-to-heat conversion layer was formed on the support. The obtained light-to-heat conversion layer has a wavelength of 700 to 1000 n.
In the range of m, there was an absorption maximum near 830 nm, and the absorbance (optical density: OD) was measured with a Macbeth densitometer to find that OD = 1.0. When the cross section of the light-to-heat conversion layer was observed with a scanning electron microscope, the film thickness was 0.3 μm on average.

3) Preparation of Coating Solution for Yellow Image Forming Layer The following components were applied to a paint shaker (Toyo Seiki Co., Ltd.)
After 2 hours dispersion treatment, the glass beads are removed,
A yellow pigment dispersion mother liquor was prepared. [Pigment-dispersed mother liquor composition] A 20% by weight solution of polyvinyl butyral (manufactured by Denki Kagaku Kogyo KK, Denka 12.6 parts butyral # 2000-L, Vicat softening point 57 ° C) Coloring material (yellow pigment (CI) .PY.14)) 24 parts ・ Dispersing aid (Solsperse S-20000, manufactured by ICI Co., Ltd.) 0.8 parts ・ n-propyl alcohol 110 parts ・ Glass beads 100 parts While stirring the following components with a stirrer: By mixing, a yellow image forming layer coating solution was prepared. [Coating liquid composition]-20 parts of the above-mentioned pigment-dispersed mother liquor-60 parts of n-propyl alcohol-Surfactant (Megafac F-176PF, 0.05 parts of Dainippon Ink and Chemicals, Inc.)

4) Formation of Yellow Image Forming Layer on Surface of Light-to-Heat Conversion Layer The above-mentioned coating solution was applied to the surface of the above-mentioned light-to-heat conversion layer for 1 minute using a wheeler. After drying for 5 minutes, the yellow image forming layer (pigment 64.2% by weight, polyvinyl butyral 3
3.7% by weight). When the absorbance (optical density: OD) of the obtained image forming layer was measured with a Macbeth densitometer, it was OD = 0.7. When measured in the same manner as described above, the film thickness was 0.4 μm on average. Through the above steps, a thermal transfer sheet in which a light-to-heat conversion layer and a yellow image forming layer were provided in this order on a support was produced.

Example 2 A light-to-heat conversion layer and a yellow image were formed on a support in the same manner as in Example 1 except that a light-to-heat conversion layer was provided using a coating solution for a light-to-heat conversion layer having the following composition. A thermal transfer sheet in which formation layers were laminated in this order was produced. [Coating liquid composition] 10 parts of photothermal conversion substance (compound represented by formula (I-8)) 200 parts of polyimide resin (Ricacoat SN-20, manufactured by Shin Nippon Rika Co., Ltd.) 200 parts of N-methyl- 2-pyrrolidone 2,000 parts-Surfactant (MegaFac F-177, Dainippon Ink and Chemicals 1 part, Industrial Co., Ltd.)

Example 3 A light-to-heat conversion layer and a yellow image were formed on a support in the same manner as in Example 1 except that a light-to-heat conversion layer was provided using a coating solution for a light-to-heat conversion layer having the following composition. A thermal transfer sheet in which formation layers were laminated in this order was produced. [Coating liquid composition] 10 parts of photothermal conversion substance (compound represented by the above general formula (I-11)) 200 parts of polyimide resin (Ricacoat PN-20, manufactured by Shin Nippon Rika Co., Ltd.) 200 parts of N-methyl- 2-pyrrolidone 2,000 parts-Surfactant (MegaFac F-177, Dainippon Ink and Chemicals 1 part, Industrial Co., Ltd.)

Comparative Example 1 A light-to-heat conversion layer and a yellow image were formed on a support in the same manner as in Example 1 except that a light-to-heat conversion layer was provided using a coating solution for a light-to-heat conversion layer having the following composition. A thermal transfer sheet in which formation layers were laminated in this order was produced. [Composition of coating liquid] Photothermal conversion material (infrared absorbing dye NK-126 (following formula), 10 parts manufactured by Nippon Kogyo Dye Co., Ltd.) Polyamide resin (polyamide acid PAA-A, 160 parts Mitsui Toatsu Chemicals, Inc.)・ Methyl ethyl ketone 1000 parts ・ 1-Methoxy-2-propanol 1000 parts ・ Surfactant (Megafac F-177, Dainippon Ink and Chemicals 1 part, manufactured by Kogyo Co., Ltd.) The above polyamic acid PAA-A (aromatic) Obtained by the reaction of a systemic tetracarboxylic dianhydride with a diamine) is 25% by weight of N, N-dimethylacetamide
Solution.

[0070]

Embedded image

Comparative Example 2 A light-to-heat conversion layer and a yellow image were formed on a support in the same manner as in Example 1 except that a light-to-heat conversion layer was provided using a coating solution for a light-to-heat conversion layer having the following composition. A thermal transfer sheet in which formation layers were laminated in this order was produced. [Coating liquid composition] 10 parts of photothermal conversion substance (compound represented by the above general formula (I-3)) Polyamide resin (polyamide acid PAA-A, 160 parts Mitsui Toatsu Chemicals, Inc.) Methyl ethyl ketone 1000 -1-methoxy-2-propanol 1000 parts-Surfactant (Megafac F-177, Dainippon Ink & Chemicals 1 part, manufactured by Kogyo Co., Ltd.)

Comparative Example 3 A light-to-heat conversion layer and a yellow image were formed on a support in the same manner as in Example 1 except that a light-to-heat conversion layer was provided using a coating solution for a light-to-heat conversion layer having the following composition. A thermal transfer sheet in which formation layers were laminated in this order was produced. [Coating liquid composition]-Photothermal conversion substance (Infrared absorbing dye NK-126, 10 parts, manufactured by Nippon Kogyo Dye Co., Ltd.)-Polyimide resin (Ricacoat SN-20, manufactured by Shin Nippon Rika Co., Ltd.) 200 parts-N-methyl -2-pyrrolidone 2,000 parts-Surfactant (Megafac F-177, Dainippon Ink and Chemicals 1 part, Industrial Co., Ltd.)

<Preparation of Image Receiving Sheet> 1) Preparation of Coating Solution for First Image Receiving Layer The following components were mixed while stirring with a stirrer to prepare a coating solution for the first image receiving layer. [Coating liquid composition]-Polyvinyl chloride (Zeon 25, manufactured by Nippon Zeon Co., Ltd.)-9 parts-Surfactant (Megafax F-177P, Dainippon Ink-0.1 parts manufactured by Chemical Industry Co., Ltd.)-Methyl ethyl ketone 130 Parts ・ Toluene 35 parts ・ Cyclohexanone 20 parts ・ Dimethylformamide 20 parts

2) Formation of First Image-Receiving Layer on Support Surface After applying the above-mentioned coating solution on one surface of the support (polyethylene terephthalate film having a thickness of 75 μm) using a wheeler, the coated product was coated with 100%. 2 ℃ in oven
After drying for 1 minute, the first image receiving layer (1 μm thick) is formed on the support.
Was formed.

3) Preparation of coating solution for second image receiving layer The following components were mixed while stirring with a stirrer to prepare a coating solution for the second image receiving layer. [Coating liquid composition]-17 parts of methyl methacrylate / ethyl acrylate / methacrylic acid copolymer (Dianal BR-77, manufactured by Mitsubishi Rayon Co., Ltd.)-17 parts of alkyl acrylate / alkyl methacrylate copolymer (Dianal BR-64・ Mitsubishi Rayon Co., Ltd.) ・ Pentaerythritol tetraacrylate 22 parts (A-TMMT, Shin-Nakamura Chemical Co., Ltd.) ・ Surfactant (Megafac F-177P, Dainippon Ink 0.4 parts Chemical Industry Co., Ltd.・ Methyl ethyl ketone 100 parts ・ Hydroquinone monomethyl ether 0.05 parts ・ 2,2-dimethoxy-2-phenylacetophenone 1.5 parts

4) Formation of the second image receiving layer on the surface of the first image receiving layer The above coating solution was applied on the surface of the first image receiving layer on the support using a wheeler, and the coated product was placed in an oven at 100 ° C. For 2 minutes to form a second image receiving layer (26 μm thick) on the first image receiving layer. Through the above steps, an image receiving sheet in which two image receiving layers were laminated on the support was produced.

<Preparation of Laminate> A laminate was prepared by laminating the second image receiving layer of the image receiving sheet and the image forming layer of the thermal transfer sheet.

<Evaluation> 1) Sensitivity measurement A rotary drum provided with a suction hole for vacuum suction was mounted on a rotating drum.
The laminated body was wound so that the image receiving sheet side was in contact with the drum surface, and the inside of the drum was evacuated to fix the laminated body to the drum surface. The above-mentioned drum is rotated, and the wavelength of 830 nm is applied from the outside to the surface of the laminate on the drum.
Are condensed so as to form a spot having a diameter of 7 μm on the surface of the light-to-heat conversion layer, and are moved while moving in the direction perpendicular to the rotation direction (main scanning direction) of the rotating drum (sub-scanning) (sub-scanning). A laser image (image) was recorded on the body.
The laser irradiation conditions are as follows. Laser power: 110 mW Main scanning speed: 4 m / sec Sub scanning pitch (sub scanning amount per rotation): 20 μm

The laminate on which the laser image recording was performed was removed from the drum, and the image receiving sheet and the thermal transfer sheet were peeled off by hand. Only the laser irradiated portion of the image (image line) forming layer received the image from the transfer sheet. Transferring to the sheet was confirmed. Observation of the transferred image with an optical microscope revealed that the laser irradiated portion was recorded linearly. The recording line width was measured, and the sensitivity was determined from the following equation. Table 1 shows the results
Shown in Sensitivity = (laser power P) / (line width d x line speed v)

2) Evaluation of fog A solid image was recorded in the same manner as described above, except that the sub-scanning pitch was changed to 10 μm so that the beam lines overlap, and the degree of turbidity of yellow of the transferred image was visually observed based on the following criteria. Was determined. Table 1 shows the results. ◎ No fog ○ Good △ No effect but cloudy × Orange cloudy ×× Green cloudy

[0081]

[Table 1]

From the results of Examples 1 to 3 described in Table 1, the photothermal conversion was performed using a polyimide resin and an indolenine compound represented by the general formula (I) having a high photothermal conversion ability as a photothermal conversion substance. When the conversion layer is formed, a high-performance photothermal conversion layer can be formed. The transfer of the photothermal conversion layer or the sublimation or decomposition of the photothermal conversion material into the image forming layer did not occur, and a good transferred image without deterioration in sensitivity and fogging was obtained. In contrast, in Comparative Examples 1 to 3, the polyimide resin and the general formula (I)
Since either one or both of the indolenine compounds represented by the following formulas were not used, good results were not obtained in both sensitivity and fog evaluation.

[0083]

According to the present invention, it is possible to provide a thermal transfer sheet which is free of fog even in a high energy printing portion and can provide a transfer image with high sensitivity.

Claims (3)

[Claims] 1. A light-to-heat conversion layer containing a light-to-heat conversion substance and a polyimide resin, a pigment and a softening point of 40 to 15 on a support.
A thermal transfer sheet comprising 30 to 70% by weight of an amorphous organic high molecular polymer in a temperature range of 0 ° C. and an image forming layer having a thickness in a range of 0.2 to 1.5 μm. Wherein the photothermal conversion material contains an indolenine-based compound represented by the following general formula (I). Embedded image (In the formula, Z represents an atomic group for forming a benzene ring, a naphthalene ring or a heteroaromatic ring, and R ¹ and R ² represent
Each independently represents an alkyl group, an alkenyl group or an aryl group, and at least one of these groups may be connected to L to form a ring. L represents a trivalent linking group, and X ⁻ represents an anion. ) 2. The compound of the formula (I) wherein L, which is a trivalent linking group, is an indolenine compound represented by the following formula (L-1) or (L-2). 4. The thermal transfer sheet according to 1. Embedded image (In the formula, Y represents a hydrogen atom or a monovalent group.) 3. The thermal transfer sheet according to claim 1, wherein a heat-sensitive release layer is provided between the light-to-heat conversion layer and the image forming layer.